Working whilst on paid leave

Is there any legal reason why I can’t work mon, tues, weds, thurs & possibly friday on agency, if I’m on paid leave from my full time job?

I know about the WTD holidays hours, but I can’t see why I can’t do this.
I need a reason cos when my TM dpwnloads digi card he’ll see what I’ve been up to. Supervisor says there is no reason not to as long as it won’t interfere with my main job.

As long as your company have no problem you wont be in breach of your contract and as long as your hours are kept legal should be no prob